Burner

ABSTRACT

An aerodynamically stabilized premix burner essentially comprises a swirl generator ( 100 ) for generating a rotating combustion air flow ( 141 ), and means for introducing at least one fuel ( 142 ) into said combustion air flow. Furthermore, the burner is equipped with means ( 112 ) for introducing an axial air flow into the center of the generated rotational flow ( 144 ). According to the invention, this axial flow can be controlled, thus enabling an influence on the position and intensity of a flame stabilizing recirculation zone ( 123 ).

TECHNICAL FIELD

[0001] The invention describes a burner for a heat generator accordingto the preamble of claim 1.

STATE OF THE ART

[0002] From EP 0 321 809, EP 0 780 629, WO 9317279, and EP 0 945 677,premixing burners are known in which a combustion air flow is introducedtangentially into a burner interior by means of a swirl generator and ismixed with fuel. At the burner outlet, the resulting vortex flow burstsopen at a jump in cross section, inducing a recirculation zone whichserves to stabilize the flame in operation of the burner.

[0003] The axial position of the recirculation zone which arises is ofcritical importance for the stabilization of the flame, and in its turnis substantially determined by the axial flow in the center of theburner. If this axial flow is too weak, the recirculation zone, and withit the flame, migrates into the burner interior. The danger then existsof a flashback of the flame and a gradual overheating of the burner. Ifon the other hand the axial flow is too strong, the recirculation zonecan detach from the burner outlet and become unstable. The consequencecan be strong, damaging, combustion pulsations or even an extinction ofthe flame.

[0004] Summarizing, the axial flow in the center of a burner of the kindmentioned at the beginning is thus of great importance for stable andsafe operation. It is therefore also known to produce a defined axialcentral flow in such burners by means of a central air injection.Nevertheless, a more or less favorable position of the recirculationzone results even in these burners in different states of operation.Thus at full load, an axial flow is desirable which is strong enough tohold the flame safely outside the burner. In contrast, at lower loadingof the burner the axial flow has to be prevented from driving therecirculation zone impermissibly far from the burner mouth; the axialimpulse of the central flow thus has to be smaller.

[0005] Solutions known from the state of the art are not capable ofsetting an optimum axial position of the recirculation zone under alloperating conditions.

SUMMARY OF THE INVENTION

[0006] The invention will provide a remedy here. The invention, ascharacterized in the claims, has as its object to provide a burner ofthe kind mentioned at the beginning with a central injection device sothat the axial impulse of the central air flow is adjustable in allregions of operation to an optimum stabilization and positioning of theflame.

[0007] This is attained according to the invention in that the saidinjection device has displaceable elements for changing a flow crosssection of the injection device.

[0008] The crucial point of the invention is thus to provide the burnerwith a variable geometry of the central injection. It is possible inthis manner to match the axial impulse of the central flow to theoperating conditions at any given time. This makes it possible to affectthe position and intensity of the recirculation zone in a targetedmanner. It is thereby possible in a particularly advantageous manner toreduce the amount of air introduced centrally at a low burner load, suchthat the recirculation zone forms very near to the burner mouth or evenpartially within the burner interior, so that a superior flame stabilityresults. At high load and high flame temperatures, in contrast, a highstability is already intrinsically inherent in the flame. Here thecentrally introduced amount of air can be increased such that therecirculation zone comes to be reliably situated a distance downstreamof the burner mouth. Thermal overloading of the burner is therebyprevented.

[0009] The use of a burner according to the invention is alsoparticularly advantageous when the flow field of the combustion air flowvaries due to changing mass flows or temperatures. Precisely suchconditions are present in the combustion chambers of gas turbines whenthe load varies. The states at the compressor outlet and the inflowconditions at the combustion chamber entrance vary considerably, due todifferent intake air mass flows and final compressor pressures.Variations of the position of the recirculation zone thereby arising canbe compensated in a burner according to the invention by an adjustmentof the geometry of the central injection device.

[0010] The embodiment of the adjustable central injection device can berealized in various ways; two preferred embodiments, particularly in thefield of gas turbine applications, are described in dependent claims 2and 3.

[0011] The invention is concerned with premixing burners, which are wellknown and familiar per se to the skilled person from the state of theart cited at the beginning. The invention can be immediately combinedwith all the constructional kinds of swirl generators and burners whichare disclosed in the documents cited there and developed from thesedocuments, and are familiar per se to the skilled person, as is onlyincompletely reflected by the preferred variants given in the dependentclaims.

[0012] The control of the central air flow can be appropriately carriedout according to different criteria. Worth mentioning and advantageoushere would be, for example, a control in dependence on the burner loador on a measured material temperature.

[0013] A further operating method results with advantageous operation inthe combustion chamber in gas turbines. Here the variable centralgeometry in combination with the operating concepts of gas turbines withpremixers, which are familiar to the skilled person, furthermore servesto ensure operation which is low in pollutants and at the same timestable and free from pulsation. Finally, a variation of the conditionscan be set for individual burners in a targeted manner, in order toprevent acoustic resonances in the combustion chamber by a detuning ofindividual burners.

BRIEF DESCRIPTION OF THE DRAWING MODES OF EMBODIMENT OF THE INVENTION

[0014] As a first preferred embodiment of the invention, a premixingburner is shown in FIG. 1, such as is known from EP 0 321 809. Theburner substantially consists of a swirl generator 100, formed by twoconical partial members 101, 102, for a combustion air flow. It can beseen from the cross section shown in FIG. 2 that the partial members 101and 102 are arranged with their axes 101 a and 102 a laterally andoppositely offset with respect to the burner axis 100 a. Tangentialinlet slots 121 are formed between the two partial members because ofthis lateral offset of the partial members. A combustion air flow 141flows through the tangential inlet slots 121 and substantiallytangentially into the internal space 122 of the swirl generator. It isof course also possible to embody such a swirl generator with anothernumber of partial members; a completely analogous structure is shown inFIG. 3 with, for example, four swirl generator partial members 101, 102,103, and 104, with the mutually offset axes 101 a, 102 a, 103 a, 104 aof the partial members. Again referring to FIG. 1, a swirl flow 144 isformed in the interior of the swirl generator, with its axial flowcomponents facing toward a downstream mouth of the swirl generator. Thepartial members 101, 102 border on a downstream end of the swirlgenerator at a front plate 108. The front plate 108 usually forms theend wall of a combustion space 50, and is frequently cooled in a mannerwhich is not shown in the Figure and is also not of substantiallyinventive. The internal space 122 of the swirl generator hassubstantially the shape of a conical frustrum, widening from an upstreamto a downstream end of the swirl generator or burner. The axial flowcross section thus formed has an abrupt widening of the cross section ata downstream end, at the opening into the combustion space 50. Abreakdown of the vortex flow 144, and the formation of a recirculationzone 123 in the region of the burner mouth, take place due to the jumpin cross section. A fuel is supplied in a suitable manner to thecombustion air flow in the swirl generator. In the embodiment example,fuel ducts 111 are arranged along the partial members in the region ofthe tangential inlet slots 121, in the axial direction of the swirlgenerator. Rows of fuel outlet bores 1111 can be seen in the embodimentexample. A fuel 142 is supplied via the fuel ducts 111, and flows viathe fuel outlet openings 1111 into the interior space 122 of the swirlgenerator 100. This kind of fuel admixing is frequently and preferablyused for gaseous fuels. Intensive mixing of the fuel 142 with thetangentially inflowing combustion air 141 takes place in the interiorspace of the swirl generator. A very homogeneous mixture of air and fuelis present in the swirl flow 144 at the outlet from the burner into thecombustion space 50. A flame from the premixed air-fuel mixture can bestabilized in the region of the recirculation zone 123. Due to the goodpremixing of air and fuel, this flame can be operated, with theprevention of stoichiometric zones and the accompanying formation of“hot spots”, with a quite high air excess: as a rule, air numbers of twoand more are found at the burner itself. Because of this comparativelycool combustion temperatures, very low emissions of nitrogen oxides canbe attained with such burners without expensive exhaust gasafter-treatment. Because of the good premixing of the fuel with thecombustion air and a good flame stabilization by means of therecirculation zone, a good degree of oxidation furthermore occurs inspite of the low combustion temperatures, and thus also low emissions ofpartially and completely uncombusted fuel, and in particular of carbonmonoxide and uncombusted hydrocarbons, but also other undesired organiccompounds. Furthermore, the purely aerodynamic flame stabilization dueto the breakdown of the vortex flow 144 (“vortex breakdown”) is found tobe advantageous. Because mechanical flame baffles are dispensed with, nomechanical components come into contact with the flame. The fearedfailure of mechanical flame baffles due to overheating, with possiblesubsequent serious accidents to machine sets, is thus excluded.Furthermore, apart from radiation the flame loses no heat to cold walls.This additionally contributes to equalization of the flame temperatureand thus low pollutant emissions and good combustion stability. Acritical factor for the operating performance of such a burner, as givenin the Figure, is the position of the recirculation zone 123. This isfurthermore essentially determined by the swirl number, roughlyspeaking, the ratio of the peripheral component to the axial componentof the vortex flow 144: if the rotational speed of the vortex flow 144is large, a wide recirculation zone is formed. Under these conditions, arobust recirculation zone is formed, situated near the burner opening,and thus a stable combustion zone is formed in operation. These areconditions which are desired in the interest of a good flame stabilityat low burner loads and thus high burner air numbers, and which also arenecessary for the stabilization of the flame, burning at comparativelylow temperatures. On the other hand, at high swirl numbers of thecombustion air flow, a region of low pressure forms along the burneraxis and, as it were, sucks the recirculation zone, and with it theflame, into the burner interior. This is however undesired at highburner loads. At full load of this burner, this operates with airnumbers in a region of 2, in the extreme case, even still underfuel-rich conditions, for example with air numbers of 1.7, 1.5 or even1.3, but air numbers being attained in each case in the region between2.5 and 2, preferably about 2.3. The combustion zone therefore clearlyhas higher temperatures than in the partial load region, in which burnerair numbers of 3 or 4 appear, and is of itself substantially morestable. A recirculation zone which is so pronounced is thus not requiredat high loads. There exists on the contrary the danger that hot gas issucked out of the combustion zone along the burner axis and into theburner. Such a flashback can on the one hand endanger the integrity ofthe burner, and in the extreme case that of a whole machine set. On theother hand, a flip-flop effect of the flame between two combustion modesinside and outside the burner can build up. Furthermore, a combustionzone spread over a larger space is desired for a high load. Summarizing,it would thus be established that here a smaller swirl number of thevortex flow 144 is desirable and realizable, which however again limitsthe operating region to small loads. In order to reduce the danger offlame flashback, it is also known to introduce an axial air flowcentrally into the burner, again negatively affecting the partial loadbehavior of the burner, since the recirculation zone is driven out ofthe burner mouth. Lastly, the constructionally predetermined flowparameters of the combustion air flow must always represent acompromise, not least because of the fact that, for example, when usedin gas turbines the inflow conditions of the combustion air to theburner vary strongly with respect to the mass flow, the temperature, andthe pressure, so that in any case it is difficult to provide a definedcombustion air flow. Here the invention proposes to introduce an axialcentral flow 145 into the center of the burner, in a known manner alongthe burner axis or the swirl generator axis 100 a. The central flow ismade variable for matching to the operating conditions. In the firstpreferred variant, an injection device 112 is situated centrally on thehead end of the burner, thus at the upstream end. The injection deviceshown here consists of a throughflow member 1121. This is substantiallya hollow-bored cylinder with an open end and an end which has a floor1124. The floor 1124 has an opening 1125 whose diameter is smaller thanthe internal diameter of the cylinder bore. The throughflow member 1121ends with the blunt open side at an inflow, that is, upstream, end ofthe burner or of the swirl generator 100, while the floor 1124 faceswith its opening toward the interior 122 of the burner. An air streamwhich flows from the inflow side toward the burner is hereby largelyconducted through the tangential inlet slots 121 tangentially into theburner as combustion air 141; however, a partial stream, dependent onthe throughflow cross section of the injection device, flows as an axialair flow 145 along the burner axis 100 a into the center of the burner,and by the additional axial impulse affects the axial position of therecirculation zone 123. An adjustable central member 1122 is insertedcoaxially into the throughflow member 1121. This member 1122 tapers atone end with a cone 1123. This cone projects at least in an axialposition of the central member into the opening of the floor of thethroughflow member. The cone 1123 obstructs the opening to differentextents by an axial adjustment of the central member 1122, and thusdefines the narrowest throughflow cross section of the injection device112. The axial central flow 145 can be controlled by an axial adjustmentof the central member, which serves as a control member, and therebyalso the position and intensity of the recirculation zone 123 can bealtered. The embodiment according to the invention of the premixingburner, known per se, thus makes it possible to match the central flowto the operating conditions of the burner. The stable and safe operatingregion of the burner is thus once more substantially widened.

[0015] In the premixing burners to which the invention preferably findsapplication, fuel is frequently also supplied centrally, this fuelsupply then finding application both as an alternative and as asupplement to the above-described fuel supply via the ducts 111. Such aburner is shown in FIG. 4. In essential elements, particularly withrespect to the swirl generator 100 and the supply of the fuel 142, theburner is completely identical to the burner shown in FIG. 1, so that adetailed description is superfluous, and the following statements can belimited to the differences of this second preferred embodiment. On theone hand, film cooling bores 1081 can be seen on the front segment 108;cooling air 148 flows through them to cool the front segment.Furthermore, a central fuel nozzle is situated on the head side, i.e.,at the upstream end, of the swirl generator. Liquid fuel or so-calledpilot gas is usually introduced via such a central nozzle into thecombustion air flow for the fuel gas operation of the burner in thelowest partial load region; both can also be combined. The fuel 146 tobe introduced centrally is supplied to the fuel nozzle 113 via a fuelduct 1131. A fuel cone 147, for example, a liquid fuel spray whichexpands from the central fuel nozzle 113 into the interior 112 of theswirl generator and which gradually mixes with the swirl flow 144further downstream, is shown in the embodiment example in FIG. 4.Usually in the real embodiment of such a burner, as shown in FIG. 4, ingas operation the main fuel is supplied as a fuel 142, as so-calledpremix gas. The central fuel supply can be used in order on the one handto supply the above-mentioned pilot gas. Furthermore, it is known toembody such burners as “dual fuel” burners, which can be operated bothwith gaseous and also with liquid fuels; in this case, a central liquidfuel nozzle finds application in practice. It is also known to implementboth liquid fuel nozzles and also pilot gas feeds in the head region ofa burner. Besides this, nozzles for water or steam injection arefrequently found in the head region of the burner, and are frequentlyused in order to attain a further reduction of nitrogen oxides emissionduring oil or pilot gas operation of the burner. In such cases veryrestricted space conditions are sometimes present in the head region,making impossible the use of a central air supply of the kind shown inthe first preferred embodiment in FIG. 1. In the second preferredembodiment a central air supply 112 arranged annularly around the fuelnozzle is therefore used. This is shown in detail in FIG. 5. The fuelduct 1131 with the fuel nozzle 113 is arranged with a substantiallyannular throughflow member 1121. The throughflow member 1121 is providedwith a number of inner control bores, arranged concentrically in anouter member 1126. The outer member 1126 is provided with a number ofouter control bores 1127, an inner control bore 1128 of the throughflowmember 1121 being allocated to each outer control bore 1127 of the outermember 1126. The central flow flows through pairs of control bores intothe annular gap formed between the fuel duct 1131 or fuel nozzle 113 andthe throughflow member 1121, and thence axially out into the internalspace 122 of the swirl generator. The outer member 1126 and thethroughflow member 1121 are arranged to be rotatable and/or axiallydisplaceable with respect to one another. The degree of overlap of innercontrol bores 1128 and outer control bores 1127, and thus also thethroughflow cross section and the mass flow of the central flow 145, canthereby be varied.

[0016] A further preferred embodiment is shown in FIG. 6. The burner 1is arranged on a combustion chamber 20, for example, of a gas turbine,and opens into a combustion space 50. Air flows from a compressor (notshown) into an air chamber 60, which is enclosed by a housing 4. Aburner hood 5 is arranged within the housing 4, and further encloses theburner 1. A plenum 55 is formed within the burner hood, and is in fluidconnection with the air chamber 60. A combustion air flow 141 flows outof the air chamber 60 into the plenum 55, and from there throughtangential inlet slots into the interior of the burner 1, where this airforms a swirl flow in the manner described hereinabove and is mixed withfuel. The burner is provided with a central injection device 112 in themanner described hereinabove. The central injection device is connectedto a central air supply duct 1129. The air chamber 60 is provided with abypass duct 61. The bypass duct 61 and the central air supply duct 1129are connected together such that a central air flow 145 can flow fromthe bypass duct 61 to the central air supply duct 1129. An adjustablethrottle element 62 is arranged in this flow path as a control elementfor the central air flow 145. Thus the central air flow can likewise bevaried as described above, and can be matched to the load conditions ofthe burner. In contrast to the embodiments of the controllable centralair injection shown in FIGS. 1 and 4, the embodiment example shown hererequires on the one hand an increased apparatus cost, since a ductsystem has to be arranged; on the other hand, the mechanicallycomparatively sensitive control element can be arranged at a suitableplace less subject to thermal load.

[0017] A special embodiment of the central air supply with a controlelement is shown in FIG. 7. Both the air bypass 61 and also the centralair supply duct 1129 open into an overflow space 63. A throttle valve 64is arranged within the overflow space. This is mounted to rotate aroundan axis, as indicated by the arrow in the drawing. The free flow crosssection of the overflow space can be changed by a rotation of thethrottle valve 64, resulting in a variation of the central air flow 145.

[0018] Based on the radial pressure equilibrium which is given by theknown equation: ${\frac{W^{2}}{r} = \rho}{\cdot \frac{p}{r}}$

[0019] where w is the circumferential speed, r is the distance from theaxis of a swirl flow, and p is the static pressure, there is always areduced pressure in the center of a swirl flow. Embodiments without aburner hood 5 would therefore also be conceivable in principle.

[0020] The burner as characterized in the preamble of the claims, isfamiliar to the skilled person in different constitutions, which differin specific embodiment from the burners shown in FIGS. 1, 4, 6 and 7,which essentially consist of a conical swirl generator. Nevertheless,all these burners are constructed according to a common principle: theyhave a swirl generator in the form of a hollow body with a longitudinalsection which encloses a swirl generator internal space. The swirlgenerator furthermore has inlet slots which extend in the direction ofthe swirl generator long axis, or inlet openings arranged in thedirection of the long axis and having a throughflow cross sectionsubstantially predetermining a tangential flow direction. Combustion airflows through these inlet openings with a strong tangential speedcomponent into the swirl generator internal space, and constitutes therea swirl flow with a certain axial component directed toward the burnermouth in the combustion space. The axial flow cross section of the swirlgenerator internal space then widens out toward the burner mouth, atleast in the region of the air inlet openings. This constitution isfavorable for attaining a constant swirl number of the swirl flow in theswirl generator internal space with an increasing combustion air massflow in the direction of the swirl generator axis. Furthermore theseburners have means to introduce fuel into the combustion air flow, whichis mixed as homogeneously as possible with the swirled combustion air inthe swirl generator and in a mixing zone, for example a mixing pipe,which can optionally be arranged downstream of the swirl generator. Ajump in cross section of the axial flow cross section is present at theexit from the burner into the combustion space. There occur here abreakdown of the swirl flow and the formation of a central recirculationzone, which can be used for the stabilization of a flame, as alreadyexpressly described above.

[0021] It is known from EP 0 780 629, which document is incorporatedinto the present application by reference, to arrange a mixing pipedownstream of the swirl generator of a burner characterized in thepreamble. The embodiment of the invention with such a burner is shown byway of example in FIG. 8. A mixing section 200 is arranged downstream ofa conical swirl generator 100, whose structure and function is notdiscussed in further detail here. The swirl generator is secured to aholder ring 210. A transition element 220 is furthermore arranged in theholder ring 210, and is provided with plural transition channels 221which transfer the swirl flow 144 generated in the swirl generator 100from the inflowing combustion air into the mixing section without asudden change of cross section. The mixing pipe 230 proper is arrangeddownstream of the transition element. A further homogenization of thecombustion air and fuel, if necessary, takes place in the mixing pipe.Based on the uniform preparation of an ignitable mixture over the wholeflow cross section of the mixing pipe, the danger exists of a flameflashing back along the low-impulse wall boundary layers in the mixingpipe. The mixing pipe is therefore provided with wall film bores 231running at an acute angle to the burner axis. An air mass 150 flowsthrough these into the mixing pipe and forms a wall film there. Thisflashback is effectively prevented by the acceleration or diminution ofthe wall boundary layers on the one hand, and the displacement ofignitable mixture from the low-impulse regions on the other hand. Themixing pipe 230 is provided at the opening into the combustion space 50with a breakaway edge 232 which likewise stabilizes the form andposition of the recirculation zone 123 forming at the burner mouth. Themixing pipe is fastened to a front segment 108 which at the same timeforms a combustion space wall and which in this example is impact cooledby means of impact cooling sheets 109 and impact cooling air 149.Besides the danger of flashback along the wall boundary layers, therealso exists here the danger of a flashback of the flame along the burneraxis 100 a under high load, or the danger of the recirculation zone 123floating away with flame instabilities at low load. In order to preventthis, the burner shown in FIG. 8 is also equipped with a controllableinjection device, not expressly shown, for an axial central flow 145,which operates as in the embodiment examples described hereinabove. Thiscan of course also be combined with a central fuel nozzle.

[0022] Burners according to the preamble of the claims are likewiseknown from WO 93/17279 and EP 0 945 677, and have cylindrical swirlgenerators with tangential combustion air inlets. In this connection itis also known to arrange a displacement member, tapering toward theburner mouth, in the interior of a cylindrical swirl generator. Thefavorable criterion given above for the axial throughflow cross sectionof the swirl generator, namely that the axial throughflow cross sectionincreases in the axial throughflow direction, is fulfilled by means ofsuch a swirl generator internal member. Embodiments of such burners areshown in FIGS. 9 and 10. The first embodiment in FIG. 9 shows theprinciple of such a burner. The mode of operation is sufficiently knownand explained in principle in connection with FIG. 1; deviating from theembodiment shown in FIG. 1 of a burner according to the invention, theembodiment shown in FIG. 9 of course has a conical compression memberwhich tapers in the combustion space 50 toward the burner mouth. Theinjection device 112 for axial central flow 145 is appropriatelyarranged in the region of the downstream end of this displacementmember. The inflow to the injection device 112 can advantageously bearranged in the interior of the displacement member; space is likewisefound there for the control means to be associated, according to theinvention, with the burner. Furthermore, central fuel injections can ofcourse be arranged here without problems, if required.

[0023]FIG. 10 shows in detail such an embodiment of the burner asexpressly described in basic form in EP 0 945 677. The displacementmember 105 is hollow, and is made blunt at its end toward the combustionspace 50. The injection device 112 for the axial central flow isarranged within the hollow displacement body 105, which is open towardthe upstream, inflow side of the burner. The mass flow of the axial flow145 can be changed by means of an axially displaceable central member1122 with a control cone 1123. The control mechanism proper, with thecone, is here arranged, for space reasons, in the upstream portion ofthe displacement member internal space. A chamber is arranged in theinterior at the downstream end of the displacement member. A fuel duct1131 leads through the hollow displacement member to this chamber, and afuel 146 is supplied by it to the chamber. This fuel can flow into theswirled combustion air flow 144 as centrally injected fuel by means ofoutlet openings 113 acting as central fuel nozzles. The position of therecirculation zone 123 can be matched to the operating conditions of theburner at any given time by the control of the axially introduced massflow 145 by means of the control cone 1123. Embodiments of the fuelinjection and the injection of the axial central flow are of course alsopossible here, in which the fuel is introduced along the burner axis 100a, and the injection device for the central flow is arranged annularly,about analogously to the embodiments shown in FIGS. 4 and 5.

[0024] The burner can of course also be provided with a cylindricalswirl generator with a mixing section following downstream of the swirlgenerator, without departing from the concept of the invention.

[0025] The use of a swirl generator with a central displacement memberalso makes it possible to shape the swirl generator itself as convergentto the mouth, but to nevertheless shape the axial throughflow crosssection of the swirl generator internal space as divergent. Thisvariant, shown in FIG. 11, makes possible a course of the transversevelocity components of the swirl flow 144 directed toward the burneraxis 100 a. Here also, the central member 105 can with advantage beprovided with an injection device 112 for the introduction of acontrollable axial central flow.

[0026] Swirl generators with tangential combustion air inlets can beconstructed in different ways. Besides the construction from severalpartial members shown in cross section in FIGS. 2 and 3, monolithicconstructions with inlet openings are also a candidate. Such anembodiment is shown in cross section in FIG. 12. The swirl generator isconstructed from a hollow cylindrical monolith. In this, inlet openings121 are machined in the form of slots running axially and tangentially,through which a combustion air flow 141 flows tangentially into theswirl generator interior 122. Fuel ducts 111 can furthermore be seen inthe form of bores which run axially and have outlet bores 1111 throughwhich a fuel 142 can flow out into the combustion air flow 141. In FIG.13, a conical swirl generator 100 with a monolithic hollow body isshown. This could of course also be cylindrical. Tangential openings,bores for example, are machined in the monolithic swirl generator andlikewise serve as tangential inlet openings 121 for a combustion airflow 141.

[0027] The embodiment examples described hereinabove are in no way to beunderstood as limitative for the invention. They are on the contrary tobe understood as illustrative and as a sketch of the multifariouspossible embodiments within the scope of the invention as characterizedin the claims.

[0028] Preferred methods for the operation of a burner according to theinvention will be apparent to the skilled person from the specific use.

[0029] A first method of operation, easy to manipulate, is shown in FIG.14. The burner 1 is operated with a fuel 142. The mass flow of this fuelis determined at a measurement point 2. The resulting mass flow signalX_(m) is processed in a control unit 3, and is converted into a controlsignal Y for the adjustment mechanism of the axial central air injectionof the burner 1.

[0030] A second embodiment, shown in FIG. 15, concerns the use of theburner according to the invention in gas turbine plants, for which theburner according to the invention is especially suitable. In the examplein FIG. 15, a compressor 10, a turbine 30, and a generator 40 arearranged on a common shaft. The compressor 10 is equipped with anadjustable front guide vane set 11. A combustion chamber 20 is arrangedin the flow path of a working medium, between the compressor 10 and theturbine 30. The combustion chamber 20 is operated with at least oneburner 1 according to the invention. A regulating signal Y is passedfrom a control unit 3 to the adjustable device for the injection of theaxial central flow. In the example shown, the control unit 3 receives apower signal X_(P), signals X_(AMB) from sensors (not shown) whichdetermine ambient conditions—temperature, moisture, pressure, etc.—ofthe ambient air, and also a signal X_(VLE) which reproduces the positionof the front guide vane set 11. A whole series of further data relevantto machine operation can be passed to the control unit 3; in particular,the generator power signal could be replaced by fuel flow signals. Thecontrol unit 3 is capable of forming from these quantities a burnerloading specific for combustion air, and to determine the control signalY from this.

[0031] A gas turbine set with a compressor 10, a turbine 30, and agenerator 40 arranged on a common shaft is again shown in FIG. 16. Thecombustion chamber 20 is shown in longitudinal section as an annularcombustion chamber which is operated with at least one burner 1according to the invention. The burner 1 is provided with a temperaturemeasurement point for the determination of the material temperature,producing a temperature signal X_(T). The combustion chamber 20 isprovided with a pulsation measuring device for the determination of thecombustion air pressure fluctuations, producing a pulsation signalX_(Puls). The signals X_(T) and X_(Puls) are passed to a control unit 3which generates a control signal Y for the control of the intensity ofthe axial central flow. When the material temperature exceeds a giventhreshold value, the central injected mass flow is increased so that theflame is driven a little away from the burner mouth, reducing the heatloading of the burner. On the other hand this can lead to an undesiredreduction of flame stability. This is determined by the pulsationmeasuring point. When the pulsation signal X_(Puls) increases, thecentral injected mass flow can be reduced, in order to increase thestability of combustion and to counter the increase of combustionpressure fluctuations. The central injection can be controlled in thismanner in dependence on relevant measured data.

[0032] It goes without saying that the given operating processes alsorepresent portions of substantially more complex, superordinate controldesigns and can be integrated into these.

[0033] It is furthermore conceivable to provide only one burner of amulti-burner system with the central air supply according to theinvention, or to operate the burners with different central air flows. Asymmetry breaking can thereby be attained in a targeted manner inmulti-burner systems, and can be used for the reduction or completeprevention of, in particular, azimuthal acoustic vibrations.

[0034] The statements hereinabove serve to the skilled person asillustrative examples for the numerous possible embodiments of theburner according to the invention characterized in the claims, and fortheir advantageous manner of operation. List of Reference Numbers   1burner   2 mass flow measurement point   3 control unit   4 housing   5burner hood  10 compressor  11 adjustable front guide vane set  20 gasturbine combustion chamber  30 turbine  40 generator  50 combustionspace  55 plenum  60 air chamber  61 air bypass  62 central air controlelement  63 overflow space  64 throttle valve  100 swirl generator  100alongitudinal axis of swirl generator, burner  102, 102, swirl generatorpartial elements  103, 104  101a, 102a, axes of swirl generator partialelements  103a, 104a  105 swirl generator internal member  108 frontplate, front segment  109 impact cooling sheet  111 fuel duct  112injection device  113 central fuel nozzle  121 tangential inlet slots 122 internal space of swirl generator  123 recirculation zone  141combustion air flow  142 fuel  144 swirl flow  145 axial central flow 146 centrally injected fuel  147 centrally evaporated fuel  148 coolingair  149 impact cooling air  150 air mass, wall film  200 mixing length 210 holder ring  220 transition element  221 transition channels  230wall film bores  232 breakaway edge 1051 chamber 1081 film coolingopenings 1111 outlet bore 1121 throughflow member 1122 central member1123 cone 1124 floor 1125 opening 1126 outer body 1127 outer controlbore 1128 inner control bore 1129 central air supply duct 1131 fuel feedduct X measured quantities Y control quantities

1. Burner for a heat generator, substantially including a swirlgenerator (100) for the tangential introduction of a combustion air flow(141) into an internal space (122) of the swirl generator, and alsomeans for the introduction of at least one fuel (142) into thecombustion air flow, and which burner has at a downstream end an abruptwidening of the cross section of an axial burner throughflow crosssection toward a combustion space (50), and which burner furthermore hasan injection device (112) for the introduction of an axial central flow(145) along a central burner axis (100 a), wherein the said injectiondevice (112) is operatively connected to adjustable elements (62, 64,1122, 1126) for the alteration of a throughflow cross section and forthe control of the mass flow of the central flow.
 2. Burner according toclaim 1, wherein the adjustable elements (1122, 1126) are directlyintegrated into the burner.
 3. Burner according to claim 1, wherein theinjection device (112) is connected to a central air supply duct (1129),and wherein the adjustable element (62, 64) is arranged in operativeconnection with an end of the central air supply duct (1129) remote fromthe injection device.
 4. Burner according to claim 3, wherein thecentral air supply duct (1129) is connected to an air bypass (61) at theend remote from the injection device, and wherein the adjustable element(62) is arranged between the central air supply duct and the air bypass.5. Burner according to claim 3, wherein the central air supply (1129) isin fluid connection with an overflow space (63); an air bypass (61)opens into the overflow space; and a throttle valve (64) acting as theadjustable element is arranged in the overflow space.
 6. Burneraccording to one of claims 1 or 2, wherein the injection device is athroughflow member (1121) arranged in the burner substantially coaxiallyof a burner axis (100 a) and having a narrowest throughflow crosssection; and a central member (1122), adjustable in its axial position,is arranged as the adjustable element and has a control cone (1123),such that the narrowest throughflow cross section of the throughflowbody defines with the control cone of the central member a throttlepoint with adjustable throughflow cross section.
 7. Burner according toone of claims 1 or 2, wherein a throughflow member (1121) is arranged asan injection device substantially coaxially of a burner axis (100 a);the throughflow member has at least one inner control bore (1128); anouter member (1126) at least partially overlapping the throughflowmember is arranged coaxially of the throughflow member, which outermember has at least one outer control bore (1127); and the throughflowmember (1121) and the outer member (1126) are arranged to bedisplaceable and/or rotatable relative to one another, such that theoverlap between the inner control bore (1128) and the outer control bore(1127) is variable.
 8. Burner according to one of claims 1-7, whereinthe axial burner throughflow cross section of the internal space (122)at least partially increases in the region of the swirl generator (100).9. Burner according to one of claims 1-8, wherein an internal space(122) of the swirl generator (100) has in longitudinal section at leastapproximately the shape of a cone.
 10. Burner according to one of claims1-8, wherein an internal space (122) of the swirl generator (100) has inlongitudinal section at least approximately a cylindrical shape. 11.Burner according to one of claims 1-10, wherein a displacement member(105) is arranged in the internal space (122) of the swirl generator(100).
 12. Burner according to claim 11, wherein the displacement member(105) tapers toward the burner mouth.
 13. Burner according to one ofclaims 1-12, wherein a mixing section (200) is arranged in thecombustion space (50) between the swirl generator (100) and the burnermouth.
 14. Burner according to claim 8 or 9, with the internal space(122) of the swirl generator having the shape of a cone widening towardthe burner mouth, wherein the injection device (112) is arranged at anupstream end, remote from the burner mouth, of the swirl generator(100).
 15. Burner according to claim 11 or 12, wherein the injectiondevice (112) is arranged at a downstream end, facing toward the burnermouth, of the displacement member (105).
 16. Burner according to one ofclaims 1-15, wherein the swirl generator is constructed from plurallaterally, mutually offset partial members (101, 102, 103, 104), betweenwhich are formed tangential inlet slots (121) for the combustion airflow (141).
 17. Burner according to one of claims 1-15, wherein theswirl generator is constituted as a monolithic hollow body, in whichtangential inlet slots and/or rows of tangential inlet openings for thecombustion air flow are machined.
 18. Burner according to one of claims1-17, for operation in a combustion chamber of a gas turbine plant. 19.Process for the operation of a burner according to one of claims 1-18,wherein the axial central flow (145) is strongly throttled at low burnerload; and the central flow is little throttled or not throttled at highburner load.
 20. Process according to claim 19, wherein the burner loadis determined by means of a fuel measurement signal (X_(m)).
 21. Processaccording to claim 19, the burner being operated in a combustion chamber(20) of a gas turbine plant, wherein the burner load is determined independence on a generator power and/or a fuel of the gas turbine plant,the setting of the front guide vane set of a compressor belonging to thegas turbine plant, and/or ambient conditions.
 22. Process for theoperation of a burner according to one of claims 1-18, wherein amaterial temperature of the burner is measured, and wherein the centralflow is controlled in dependence on the measured material temperature.23. Process for the operation of a burner according to one of claims1-18 in a combustion chamber (20) of a gas turbine plant, whereincombustion pulsations are measured, and wherein the central flow iscontrolled in dependence on the measured combustion pulsations. 24.Process for the operation of a burner according to one of claims 1-18 ina multi-burner system of a gas turbine, wherein the central flow ofindividual burners is controlled in dependence on the measuredcombustion pulsations.